OpenAPI / Swagger documentation exists

Without an OpenAPI spec, every external consumer — a mobile app, a third-party integration, a future backend service — must reverse-engineer your API from network traffic or source code. This directly undermines ISO-25010:2011 compatibility.interoperability and raises integration time proportionally with API surface area. Internal teams suffer the same friction: undocumented APIs attract inconsistent usage patterns and make breaking-change detection impossible without grep-and-hope. A spec is also the prerequisite for automated client SDK generation, contract testing, and mock servers.

Generate an OpenAPI spec from your existing Zod validation schemas rather than writing it by hand. If you're already using Zod (recommended), zod-to-openapi converts schemas you already have:

// src/openapi.ts
import { OpenAPIRegistry, OpenApiGeneratorV3 } from '@asteasolutions/zod-to-openapi'

const registry = new OpenAPIRegistry()
registry.registerPath({
  method: 'post',
  path: '/api/v1/users',
  request: { body: { content: { 'application/json': { schema: createUserSchema } } } },
  responses: { 200: { description: 'User created' } },
})

Commit the generated openapi.yaml to the repo and serve it at /api/docs in development. For ts-rest, the spec generates automatically from your contract definitions — no extra work.